Metal-coating furnace



June 4, 1968 K. FRITZ METAL-COATING FURNACE Filed March 3, 1964 KARL FRITZ INVENTOR.

Fig.2

BY .zualzm, was: 6' flail"! 3,336,720 METAL-CQATING FURNACE Karl Fritz, Feithstrasse 25, Hagen, Germany Filed Mar. 3, 1%4, Ser. No. 349,027 Claims priority, application Germany, Mar. 8, 1953,

39,195 8 Claims. (6i. 263-44) ABSTRAQT 6F THE DiSfILGSURE A furnace for the zinc and aluminum dip-coating of sheet-metal whose upwardly open trough is heated by a mantle disposed above and close to the surface of the melt but which has a separate foundation in coextensive contact with the trough and provided with cooling ducts through which a liquid is circulated. The trough is maintained at a temperature of about 550 C. and the cooling fluid is circulated through the concrete foundation so as to maintain the temperature therewithin at a level between 80 and 90 C.

My present invention relates to metal-coating furnaces or ovens and, more particularly, to zinc and aluminum furnaces for the so-called hot dipping of metallic sheets in galvanizing processes or the like operating with molten metals.

Furnaces for the hot dipping or galvanizing of metallic sheets with aluminum or zinc protective layers generally comprise a refractory trough for the molten zinc or aluminum through which the sheet metal is passed and which may be heated from above with the aid of burners or the like. For the most part, such furnaces have a pan or trough which is composed of a ceramic material in the form of bricks, blocks or the like and an insulating layer, also of ceramic material, surrounding the trough, the entire trough structure being mounted upon a foundation of concrete or the like. Such furnaces can be operated for uninterrupted stretches ranging from months to years and have been characterized heretofore by the formation in the masonry wall of the trough of crevices and spalling, the melt penetrating into the crevices and recesses and further accelerating the deterioration of the wall of the trough. Moreover, these earlier structures are also characterized by a settling of the foundation, especially when the latter is supported in sandy soils, apparently as a consequence of the desiccation of the surrounding ground by the high temperatrues of the foundation. Both the r aforementioned disadvantages have been discovered to be derived from an excessive heat transfer from the moltenmetal trough to the concrete foundation.

It is the principal object of the present invention, therefore, to provide a method of operating a metal-coating furnace wherein the aforementioned disadvantages can be avoided and the heating of the concrete foundation of the furnace to high temperatures can be prevented.

A further object of this invention is to provide a furnace of the character described wherein excessive heat transfer from the trough to the foundation is prevented.

I have found that foregoing disadvantages of earlier structures can be eliminated when excessive heat transfer to the foundation in such manner as to elevate its temperature above a predetermined maximum level is avoided by a method which involves the cooling of the foundation with liquid or gaseous cooling medium to a emperature which does not exceed 100 C. and which preferably is below this temperature, i.e. between 80 and 100 C. For this purpose, the foundation can be provided with a plurality of cooling channels in the form of canals formed integrally in the concrete foundation or 3,3%,?2d Patented June 4, 1968 the tubes embedded therein, the tubes being provided with means for supplying the cooling fluid to them and removing the cooling fluid therefrom.

According to a more specific feature of the present invention, the longtiudinally extending furnace is mounted upon and partly in a foundation formed with an array of lineal cooling channels below the interface of the foundation and the molten-metal trough, the cooling channels extending generally transversely of the major dimension (i.e. the longitudinal direction) of the trough and communicating at their extremities with inlet and outlet manifold means extending longitudinally in the foundation. Thus, the cooling channels may include a multiplicity of parallel tubes or canals formed in the concrete foundation and a pair of conduits at the opposite extremities of the cooling channels extending perpendicularly thereto for supplying the gaseous or liquid medium to the channels and removing the medium therefrom. In general, it has been found to be advisable that the cooling channels extend substantially parallel to the general direction of flow of the cooling medium. The channels themselves may be passages formed upon the casting of the concrete foundation or tubes embedded therein, whereas the inlet and outlet conduits are preferably troughs integrally provided in the concrete foundation and, if desired, formed with inlet and/or outlet tubes passing through a cover portion overlying the inlet and outlet troughs.

I have found that, surprisingly, certain essential critical relationships between the diameters of the cooling channels and their spacing must be observed if optimum cooling of the foundation is to be obtained. Thus, it may be noted that the array of parallel cooling channels should consist of individual passages whose diameter (inner diameter of the tubes) and the spacing of the channels one from the other are in the ratio of substantially 1:3 to 1:5 and the distance of the array from the interface of the foundation and the molten metal trough is in a ratio with the diameter of the cooling passages of substantially 1:1 to 2:1.

According to a further feature of the present invention the inlet and/or outlet tubes are provided with flowcontrol means adapted to regulate the rate at which the cooling fluid is passed through the cooling channels. A temperature-responsive means is located in heat-exchanging relationship with the molten-metal trough and preferably is disposed between the array of cooling passages and the interface between the molten-metal-trough structure and the foundation while circuit means controlled by the temperaturesensitive device is provided for operating the flow-control. means to maintain a substantially constant temperature of the formation as previously described.

When the measures described above are taken, there is found to be little desiccation of the ground supporting the foundation so that no settling of the furnace occurs for the most part. Moreover, spa ling of the molten-metaltrough masonry is substantially reduced as is the tendency toward the formation of crevices and the penetration of molten metal into these crevices. In general, the trough walls have been found to have a usable life ranging upwardly from 10% greater than the usable life of the walls of troughs whose foundations are not provided with cooling means of the character described.

The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying rawing in which:

FIG. 1 is a transverse cross-sectional view through a hot-dipping metal-coating furnace according to the present invention;

PEG. 2 is a longitudinal cross-sectional view taken along the line 11-11 of FIG. 1.

In the drawing, I show a furnace for the hot-dipping of metals which comprises a trough 2 composed of blocks of a ceramic material and containing a molten-metal bath 3 which can be zinc or aluminum. The bath is surmounted by a cover in the form of a downwardly open semicylindrical heating mantle 4 in whose cavity 4 a combustion of hydrocarbon gases can be carried out at a burner for obtaining the temperature necessary to maintain the metal within the trough in a molten state. The mantle 4 is composed of a refractory material and is, in turn, covered by an insulating layer 4a.

The masonry trough is provided with an insulating layer 1 also of ceramic material, the layer being supported laterally by the metallic channel-shaped walls 1. The trough 2 and its insulating layer 1 rest upon the concrete foundation 5 with which it forms an interface 5', across which a heat transfer takes place between the trough structure ll, 2 and the concrete foundation. The layer surrounds a planar array of tubes 6 embedded in the concrete of the foundation, these tubes extending transversely to the major or longitudinal dimension of the furnace and constituting spaced but parallel cooling channels. The metallic sheet material to be coated may be passed through the bath 3 as indicated by dot-dash lines in FIG. 1 which represent the means for passing the sheet material through the bath.

The concrete foundation 5 is surrounded by a steel supporting structure 5" and is formed with a pair of longitudinally extending conduit troughs or channels '7, 7' serving as the inlet and outlet manifolds for the tubes 6 with which they communicate, respectively. The outlet channel '7' can be covered with a grate 9 to permit the escape of air or other gaseous fluids when this medium serves for cooling of the foundation and/or provided with an overflow pipe 10 for discharging liquid coolants from the canal. It may be noted that, in either case, the mouth or outlet for the fluid from the channel 7 is disposed above the tubes e and, preferably, above the interface 5. The grate extends the full length of the trough 7 so that there is little impediment to the escape of coolants.

A thermostatic device if, e.g. in the form of a pyrometer, is provided with a sensing element 11' intermediate the array of pipes 6 and the interface 5"; this temperaturesensitive device can serve to energize a relay 11 which, when activated, electrically operates a valve 8' in the coolant supply pipe 8 for controllin the passage of the coolant through the pipes 6; other control means can, of course, also be provided.

Example A furnace for the galvanizing of iron parts by hot dipping in molten zinc and of the general construction illustrated in FIGS. 1 and 2 is maintained at a temperature of approximately 450 C. by combustion of gases Within the heating mantle 4 in the usual manner. The tubes 6 each have an inner diameter of 5-6 cm. and are spaced apart by a distance of 4 cm. below the interface 5. Five tubes are provided per meter of length of the trough structure 1, 2 and the tubes are embedded in the concrete. A thermostat having this sensing element disposed between the pipes 6 and the interface 5 is set at 85 C. (:L-S" C.) and controls a valve which starts and stops the flow of water to the pipes at a pressure of 3 kg./ cm.-, the water being at a temperature of 15 C. (15 C.) prior to introduction at the inlet pipe. Temperatures taken by means of thermocouples within the concrete mass show that its temperature ranges between 80 and 90 C.; there is no settling of the foundation. When a similar furnace without coolant tubes is employed, the walls 2 and 5 of the trough structure receive, in case of settlement of the foundation, cracks and liquid zinc or aluminum flows out.

The invention described and illustrated is believed to admit of many modifications within the ability of persons skilled in the art, all such modifications being considered within the spirit and scope of the appended claims.

i claim:

1. A furnace for the hot coating of sheet metal with a bath of zinc or aluminum comprising a foundation, a ceramic trough structure mounted directly on and in co extensive contact with said foundation while being partly received therein, a cover partly overlying said trough and lying close to the surface of a static molten-metal bath therein, means in said cover for heating said bath, means for passing sheet metal through said bath for coating with the molten metal thereof, cooling means including a plurality of channels formed in said foundation for passing a cooling fluid through at least a portion of said foundation for reducing the temperature of said foundation below that of said trough, inlet means for supplying said fluid to said channels and outlet means for discharging said fluid from said channels.

2. A furnace as defined in claim 1 wherein said foundation is composed of concrete and said trough structure includes a ceramic trough-forming portion and an insulating layer of ceramic material interposed between said trough-forming portion and said foundation, said channels forming a generally planar array of substantially parallel passages, said inlet and outlet means including respec ive manifolds communicating with said passages.

3. A furnace as defined in claim 2 wherein said channels are tubes embedded in the concrete foundation.

4. A furnace as defined in claim 2 wherein said channels are passages molded into said concrete foundation.

5. A furnace as defined in claim 2 wherein said trough extends longitudinally along said foundation and said passages extend transversely thereto, said manifolds extending longitudinally in said foundation and communicating with said passages for directing said cooling fluid transversely to said trough.

d. A furnace as defined in claim 5 wherein said passages are of substantially equal diameter and the diameter of said passages is in a ratio to the spacing of adjacent channels from one another of substantially 1.3 to 1.5.

7. A furnace as defined in claim 6 wherein said trough structure and said foundation have a common interface extending substantially parallel to said array of channels, the distance between said array of channels and said interface being in a ratio to said diameter of substantially 1:1 to 2:1.

8. A furnace as defined in claim 7, further comprising control means connected with at least one of said manifolds and temperature-sensitive means in heat-exchanging relationship with said trough structure and operatively connected with said control means for regulating the flow of cooling fluid through said passages to maintain a substantially constant temperature of said foundation, said temperature-sensitive means being provided with a thermally responsive element disposed between said surface and said array, said control means including valve means and an electric circuit provided with relay means for operating said valve means, said element being a pyrometer connected in circuit with said relay means.

References Cited UNITED STATES PATENTS 1,047,521 12/1912 Hcrreshoif 263-44 2,199,355 4/1940 Underwood 26344 2,514,871 7/1950 Jordan 263-44 2,671,658 3/1954 Moore 263-44 X FREDERICK L. MATTESON, Jrc, Primary Examiner.

D. A. TAMBURRO, A. D. HERRMANN,

Assistant Examiners. 

